Prosthetic hand



1952 .1. E. CONZELMAN, JR, ET AL 82, 34

PROSTHETIC HAND 5 Sheets-Sheet 2 Filed June 28, 1948 m [Q N v/ m 5 N)mo/m eo i w 5 v i co m m N o m v 'lm/s/vroe JOHN E. co/vzamn/v, Je.

HERBERT B. ELL/6' CZHVTON LU. O'BQ/E'N Jan- 15, 1 2 .1. E. CONZELMAN,JR., ET AL 2,582,234

PROSTHETIC HAND Filed June 28, 1948 5 Sheets-Sheet 5 lOl wins/r025, JOHNE. CONZL-ZMHN, Je. HEQBEQT 5. ZL/S yam ro/v 40. 0952/5 ,QTTOENEV Jan.15, 1952 Filed June 28, 1948 J. E. CONZELMAN, JR, ET AL PROSTHETIC HAND5 Sheets-Sheet 4 IIII'IVI run v1.1.

wm-wraes, JOHN E. CONZELMfl/V, J2. HEQBEQT 5. aus CLHVTON w. 0 Be/EN V 5WM HTTOENEV atented jan. 15, 1952 PROSTH-ETIC HANIS J ohn E. Conzelman,Jr., Sierra Madre, Herbert H.- Ellis, La Canada, and Clayton WLOBrien,Los' Angeles, Calif.

Application June 28, 1948 Serial No. 35,634

2 Claims.

Th s invention relates to prosthetic devices,

and more particularly to prosthetic hands, and

has as an object the provision of a serviceable prosthesis of naturalappearance as a replacement for a hand which has been amputated at orabove the wrist.

'Modern surgery and intensive eiforts to rehabilitate persons who havelost parts of their limbs through warfare, disease, or accident, haveresulted in great advances in the science of prosthetics. The immobilegloved hand, incapable of useful action, and the unsightly thoughremarkably efficient hooks are both tending to. give place to artificialhands which combine appearance and utility to a degree materiallyrestoring the morale and'the capabilities of the amputee. The technicalimprovements in the prosthetic hands themselves have been accompanied byadvances in the controls by which the devices are operated, one of themost notable of such steps being that ofcineplasty, or utilization ofthe muscles within a stump to impart some of their normal function to anappropriateprosthesis. Arrangements of harnesses operated by movementsof the shoulders. and of the stump relatively to the shoulder have alsobeen improved until a, greater number of controlled movements of theprosthesis are now possible than could'be obtained with earlierharnesses.

To talge'full advantage of the above-mentioned advances in theprosthetic controls, the artificial hands operated thereby must befairly complicated articulated mechanisms. To relieve muscular strainand to obviate the necessity of maintainiri the upper arms and shouldersin awkward. positions, the hands require .locking devices by which agrip once exerted may be held without undue effort. It is furthermoredesirable, that the grip should be. as powerful as, the occasion mayrequire. Yet in the absence of tactile sensation, the powerexerted mayordinarily be judged only by muscular fatigue, which of course isto beavoided. And while each added feature of utility increases the number,and often the bulk, oi the parts of theprosthesis, it remains arequirement that the prosthesis shall notbe excessively heavy and shallbe of natural ppear ce- 'It is accordingly a further object of ourinvention to provide a prosthetic hand sufficiently articulate to affordan adequate grip uponan ob.- ject and designed to move in a mannerclosely simulating the movement. of, a natural hand.

Another object of the invention is to provide a prosthetic hand havinga. minimum system of operating'linkage consistent with affording anadequate grip, and with that system so disposed as to place'the centerof gravity of the prosthesis high towards the elbow, to minimize theefiective or apparent weight of the prosthesis.

Yet another object'of the inventionis to provide a prosthetichand havinga simple and effective locking device'by which a grip once establishedupon an object may be maintained without further muscular effort andincluding in the locking device means for tensing the grip soestablished and locked. 7

Still another object of the invention is-to provide a prosthetichandwhich maybe easily and quicklydetached from the forearm stump orattached thereto and-which has its control mechanism so disposed andarranged that it maybe actuated either by shoulder harness orby cordagecineplastica-lly securedto one or more of the muscles of the stump. v

A further object of the invention is to provide a prosthetic hand havinga force-multiplying mechanism permitting rapid articulation of thefingers in gripping direction in the absence of resistance, andincreasing the applicable force with reduced but not terminated motionwhen a predetermined resistance is encountered, whereby the prosthesisis particularly adapted to the limits of motion and force imposed byoineplastic operation.

It is another object of the invention to provide a prosthetic handhaving a sensor -device for transmitting an indication of contact to asensitivepart of the amputees body.

Still another object of the invention is to provide a prosthetichand inwhich the aforesaid sensory device.- not only transmits. an indicationof contact, but also indicates to the amputee the degree of. pressureexerted. by the. hand.

The inventionpcssesses other objectsand features ofadvantage; some ofwhich, with .the foregoing, will be set orth in the followingdescription of the preferred forms of invention which are illustrated inthe drawings accompanying and forming part of the. specification. It isto be understood that. I do not. limit myself to they showing made bythe said drawingsand description, as I may adopt variations of thepreferred forms within the scope of my invention as set forth in theclaims.

Referring to the drawings:

Figure l is an elevational view in perspective of a prosthetic handembodying the principles of this invention, the hand being shown in theclamped or gripping position. t

Figure 2 is a longitudinal vertical sectional view through the wristportion of the hand shown in Figure 1, and on an enlarged scale, theplane of section being indicated by the line 2-2 of Figure 1, with thedirection of view as indicated, and is illustrative of a quick-lockingmechanism controlling a bayonet look by which the hand is secured to thestump cuff.

Figure 3 is a fragment of the view of Figure 2, with the quick-lockingmechanism shown in the unlocking position Figure 4 is a transversesection taken on the plane of section indicated by the line 44 of Figure2, at a slightly reduced scale and with the direction of view asindicated, and shows the hand or distal member of the bayonet lock.

Figure 5 is a transverse section taken on substantially the same line asFigure 4, but in the opposite direction of view as indicated by thearrows 55 of Figure 2, showing the forearm or proximal member of thebayonet lock.

Figure 6 is a detail in exploded perspective illustrating the clutch orconnecting joint between the proximal and distal portions of theoperating plunger.

Figure '7 is a top plan view of the prosthesis, partly in section andwith parts broken away to show the internal operating mechanism, theparts being in the gripping position as in Figure 1, and the extendedposition of the actuating lever being shown in broken lines.

Figure 8 is a longitudinal vertical sectional view on an enlarged scaletaken on the line 8-8 of Figure 7, showing the operating plunger and itsconnected linkage in the retracted or gripping position corresponding toFigures 1 and 7.

Figure 9 is a longitudinal vertical sectional view similar to Figure 8,but with the operating plunger in its advanced or released position topermit extension of the fingers.

Figure 10 is a longitudinal vertical sectional view taken on the linell)l0 of Figure '7, showing a finger-locking and grip-boosting mechanismin locking and boosting position.

Figure 11 is a fragmentary sectional View similar to Figure 10, butshowing the mechanism released.

Figure 12 is another view similar to Figures 10 and 11, and showing themechanism in fingerlocking position, but not constrained to boost thegrip of the fingers.

Figure 13 is a longitudinal vertical sectional view illustrative of thefinger articulation and the articulating linkage, taken on the line l3l3of Figure '7.

Figure 14 is an elevational view of a force-multiplier interposedbetween the operating harness and the operating lever of the prothesisfor increasing the power applicable to the finger grip, the parts beingshown in relaxed position.

Figure 15 is a view similar to Figure 14, in which the parts of theforce-multiplier are in tensed position.

Figure 16 is a view similar to Figure 14, illustrating a modified formof force-multipler.

Figure 17 is a perspective view of our prosthetic hand, illustrating apreferred form of sensory device.

Figure 18 is a sectional view on an enlarged scale, taken in part on theline l8l8 of Figure 17, and in part illustrative of the finger-tipmechanism.

Figure 19 is a perspective view similar to Figure 1'7, and showing amodified form of sensory device.

Figure 20 is a schematic view of the electrical circuit of the deviceshown in Figure 19.

Specifically describing the preferred embodiment of our invention, andmore particularly referring for the moment to Figures 1 to '7, ourimproved prosthetic hand comprises a casing 25 having the general formof the upper part of the human hand from the proximal digital joints tothe wrist and including a thumb 26 formed integrall therewith in aposition of fixed opposition to the fingers. A digital casing 21, forminthe third and fourth fingers 28 and 29 and the proximal phalanges 30 and3| of the index finger 32 and second finger 33, is pivotally secured toa knuckle bar 34 within the casing 25 by pivot screws 35. The proximalportion of the casing 27, representative of the proximal knuckles of thefingers, is slightly expanded in the form of a transverse semi-cylinder36 which fits within the open distal end 3'! of the casing 25 andpermits relative movement of the casings 25 and 2? while forming asubstantially closed joint of natural appearance (see Figure 13). Thedistal phalanges 38 and 39 of the index and second fingers respectivelyare formed separately from the digital casing 21 and are connectedthereto by knuckle rods 40 pivoting on pins 4!. The phalanges 38 and 39are belled to form socket members 12 mating with balls 43 on the ends ofthe phalanges 3i and 3| in ball and socket joints. .Thus there isprovided a complete semblance of a natural hand with provision forarticulation of all four fingers as a unit at the proximal knuckles andof the index and second fingers at the medial knuckles, and completelyenclosing and concealing the hereinafter described linkage and operatingmechanism extending thereinto.

It will be understood that the hand described above may be, and normallywill be, encased in a cosmetic glove which will give a further life-likeappearance and will further conceal the articulated joints, but as sucha glove forms no part of this invention, it is omitted from the drawingsfor clarity of illustration.

A stump cuff 45 is secured to the forearm stump of the amputee, as bylacing or other conventional means, and ha a casing 46 which extendsforwardly to join the casing 25. The rearward end of the casing 25 hasan end plate 41 held thereto by screws 48 and to which is secured themale member 49 of a bayonet lock (Figures 4 and 5). The female member 50of the bayonet lock is secured to an end plate 5| attached to the casing46. The male member 49 has a slot 52 in that portion of its periphery,preferably the upper portion, which is exposed when the bayonet lock isengaged. The female member 58 supports slidably a pin 53, engageablewith the slot 52 to prevent the bayonet look from being accidentallyturned to a" disengaging position. The pin 53 is urged to engage theslot 52 by a spring 54 and i manipulated by a handle 55. The handle 55extends through an angulated slot 56 in the casing 46 which permits itto be moved forwardly into locking position, as urged by the spring 54,or to be retracted and moved to the lateral channel of the slot 56, asshown in Figure 3, there to be retained while the amputee uses his otherhand to manipulate the bayonet lock.

The casing 46 serves as a housing for that portion of the prothesisoperating mechanism to which muscular force is primarily applied. Asherein illustrated, and more particularly shown in Figure 7, thisprimary operating mechanism comprises a lever 58 pivoted on a fulcrumpin 59 secured to the stump cuff 4.5 and movable in rearward and forwarddirections by means of a cable 60 in opposition to a spring 6 l. Thecable 60 may lead to a muscle-motor device such as a shoulder harness,not shown,-by which it may be tensed by suitably shrugging theshoulders. Alternatively, the cable 6% may lead to a cineplastic muscletunnel in the forearm of the amputee, in which event the lever 58 mayprotrude, as shown, through a slot 62 in the casing 46 and the cable 60may re-enter the casing 46 or the stump cuff 45 A at an appropriatepoint, or the lever and cable may be entirely housed within the casing46 and the stump cuff 45. The hereinafter described force-multiplyingmechanism may also be housed within the casing 56, with the cable 60forming a part thereof or being attached to the chain thereof,particularly in the event of cineplastic motivation of the prosthesis.When shoulder harness is used to actuate the prosthesis, theforce-multiplying mechanism may be located adjacent the upper arm inorder to lessen the weight of distal portions of the arm.

The lever 58 actuates a push rod 63, pivotally secured thereto by a pin64 and urged to assume a forward position by the spring 6|, as shown inbroken line in Figure 7. The rod 63 carries on its forward end thefemale member of a clutch or bayonet lock, shown at 65 in Figure 6,which is engageable with a male member 66 on the rearward end of aplunger 61 mounted in the casing 25. The male members 56 and 49 of theclutch and the connecting bayonet lock are so disposed as to engagesimultaneously with the female members 65 and 5t, so that the operationof connecting the casing 25 to the casing 46 also connects the plunger61 to the primary operating mechanism housed in the casing 46, and theplunger is also secured against accidental release by the locking actionof the locking pin 53 in the slot 52.

Viewing now Figures 8 and 9, and also Figures 2and 7, it will be seenthat the plunger 61 is connected by a connecting rod 69 to an arcuaterack preferably in the form of a toothed quadrant II! which pivots upona shaft ll transversely mounted within the casing 25 upon brackets 12secured to the end plate 41. The connecting rod 69 is pivotally attachedto the plunger 6'! and the l quadrant ID by connecting rod pins 13 and14, respectively. The hub portion 15 of the quadrant 70 has a pair ofupstanding arms 16 between which, on a pivot pin 11, a link 18 ismounted. The link 18 extends forwardly inside the casing 25 andtransmits movement of the quadrant to the digital casing 27, to which itis connected, and thence to the movable phalanges 3S and 39.

The link 18 is connected at its forward end to an ear 8!! integral withthe casing 21 by. means of a pivot pin BI and an adjustable fitting 82.The fitting 62 is threaded into the end of the link 18 so as to makepossible a variation in the effective length of the link and thus tovary the initial or extended angle between the casings 25.,and 21. Theknuckle bar 34 has three forwardly extending lugs, of which the twoouter lugs 83 and 84, respectively adjacent the little finger 29 and theindex finger 32, receive the screw 35 upon which the digital casing 2!is pivoted. The pivot pin 8| lies above the axis of the screws 35, andforward pressure upon it by the link it will consequently cause thecasing 21 to rotate towards the thumb 26.

The lug 84' and the intermediate lug 85 also pivotally receive theproximal ends of links .85 and b'l'extending to the distal phalanges $38and 3,9; of the index finger and second finger 32 and 33. As shown inFigure 13, the lug extends and when the pins 4| are swung downwardly,

the pivot points 59 are swung downwardly in arcs intersecting andpassing inwardly of the arcs through which the pins 4! move.Consequently, downward arcuate movement of the digital casing 21 resultsin relative downward arcuate movement of the distal phalanges 38 and 39and at an increasing rate of relative movement. The index and secondfingers '32 and 33 are thus caused to flex at theirmedial joints and toclose rapidly towards the thumb'26, of course flexing oppositely anddeparting from the thumb when the direction of movement of the digitalcasing 27 is reversed.

The grip established between the fingers 32 and E3 and the thumb 26utilizes the palmar surfaces of the fingers and thumb to grasp anobject. Surface contact, rather than line or point contact, is dependedupon as a holding means, and the contacting surfaces may be providedwith patches of rubber or latex, as shown at 99 in Figure 1, tofacilitate a secure grasp.

Having reference now to Figures 10, 11, and 12, a locking device isprovided for locking the fingers in any desired position, to relieve thestrain upon the muscles, and also for increasing the tension of the gripin the locked position. An arm 9! is rotatably mounted upon the shaft Hand is biased by a coiled spring 92 to rotate in a clockwise direction,as seen in Figures 10 to 12. A bell crank lever 93 is pivoted on a pin94 secured in one of the brackets l2; connecting the arm 9! with thebell crank lever 93 is a double linkage comprising a pawl 95 toothed tomesh with the quadrant Hi and disposed in the same plane therewith andpivotally mounted on the distal end of the arm Bl by a pin '96, and alink 9'! pivotally mounted on the shorter arm of the bell crank lever 93by a pin 98 and con-.

nected pivotally to an arm 99 of the pawl 95 by a pin ldil. The spring92 urges the arm 9! into contact with a stop bar till, eccentricallymounted on the bracket 12 and adjustable to regulate the amount ofclockwise motion permitted to the arm 9|. A second spring I82, havingone end affixed to the arm 9! and its other end bearing against the pinltd, urges the pawl 85 to a position out of mesh with the quadrant Hi.

In Figure 11, the quadrant Hi and the upstanding arm 16 indicate bytheir position that the fingers of the prosthesis are relaxed andextended. It will be seen that the spring 92 has brought the arm 9| intocontact with the stop bar Hi! and that the spring 32 has caused the pawl85 to disengage from the teeth of the quad-- rant F9 and to assume aposition governed by the length of the link 97. The pawl 95 is stillfree to pivot upon the pin 95, and counter-clockwise rotation of thebell crank lever 93 will cause the pawl to pivot counter-clockwise, butthe rotation will be resisted by the spring 192,.

In Figure 12', the quadrant I is shown as having rotated in thedirection consistent with closing the grip of the prosthesis and thebell crank lever 93 is shown as having been rotated slightlycounter-clockwise, causing the pawl 95 to mesh with the quadrant I0.Meshing of the pawl 95 with the quadrant It in efiect freezes the pawlin relation to the arm 9|, so that further rotation of the pawl can beeffected only by rotating the pawl, the arm SI, and the quadrant 10, asa unit. Conversely, the quadrant I0, which is in the actuating chain oflinkage to the digital casing 21 and to the fingers 32 and 33, cannotmove without causing movement of the pawl 95 and the arm 9|. Rotation ofthe quadrant I0 consistent with opening the grip would be in a clockwisedirection and would call for rotating the arm 9| clockwise as a part ofthe frozen unit. But the arm 9| still rests against the stop bar IOI andcannot rotate clockwise. The prosthesis is therefore locked in theposition which the digital casing 27 and the fingers 32 and 33 haveassumed. The only force effective to unlock the prosthesis other thanmovement of the bell crank lever 93, is the spring I02 which continuesto urge disengagement of the pawl 95 from the quadrant I0. However, suchdisengagement cannot be accomplished without moving the link 91 and thebell crank lever 93, and the angle of leverage applicable to the bellcrank lever through the link is so slight that the force of the springI02 is substantially offset by the weight of the bell crank lever andthe friction on the pins 94, 80, 98, and I90. Moreover, the pawl 95tends to freeze to the quadrant 'Iii because of the friction of themultiplicity of teeth by which these members are engaged, and be- 4cause the tangential thrust of the quadrant on the more distal teeth ofthe pawl is substantially directed at the pin 96 upon which the pawlwould normally pivot.

To positively secure the locked grip of the prosthesis and to furthertighten the grip, the bell crank lever 93 may be moved to the positionshown in Figure 10. It will be observed that this movement has causedcounter-clockwise rotation of the above-described frozen unit ofquadrant l0, arm 9| and pawl 95, all rotating about the fixed shaft "EIas an axis in response to fulcrum action on the fixed pin 94, andpulling the arm 9| out of contact with the stop bar IN. The smallcounter-clockwise rotation of the quadrant '50 so effected acts throughthe upstanding arm F 3 and the link I8 to cause a slight furthergrip-tensing movement of the digital casing 2'5 and the fingers 32 and33. Furthermore, the pin 98 having now moved across the center lineconnecting the fulcrum pin 94 with the pin 95, a positive look will havebeen established upon the prosthesis which cannot relax its grip withoutfirst further tightening it.

It will be understood that the object in looking the prohthesis byeither the substantial lock described in connection with Figure 12 orthe positive lock described in connection with Figure 10, is to relievethe amputee of the necessity of maintaining tensed muscles in order tomaintain a grip. It will further be seen that the amount of additionaltensing of the grip during the positive locking operation depends uponthe distance which the arm 9| moves away from the stop bar IOI. Thefurthermost counter-clockwise position which the arm SI may assume isdetermined by the form and arrangement of the linkage connecting the twofixed pivotal points, i. e., the pin 8 04 and the shaft II. The distancewhich the arm 9| moves to attain this furthermost position depends uponits starting point, which in turn depends upon the position of the stopbar IOI. By orienting the stop bar to increase or to decrease the totalpermitted angular movement of the arm 9|, the added tensing of the gripof the prosthesis may be increased or decreased. Thus by adjusting thestop bar IOI so that its highest shoulder, indicated at I03 in Figure10, is directed towards the arm 9|, the arm will be held at all times atits counter-clockwise limit of movement, and no tensing of the grip willoccur when the prosthesis is locked. This adjustment is of greatimportance when incompressible objects are to be grasped and held forsome period of time, as it prevents the necessity of placing excessivestrain upon the grasping surfaces and the operating linkages of theprosthesis in order to release the grip.

The hereinbefore mentioned force-multiplying device is illustrated in apreferred form in Figures l4 and 15, and in a modified embodiment inFigure 16. Referring to Figure 14, a support frame I04 is pivotallymounted on a pivot I05 upon a base member I06 which as heretofore statedmay be within the forearm casing 46 and secured thereto, or may besecured to some part of the amputees body, such as the upper arm. Theframe I04 supports a sprocket I01 of fixed relative position determinedby the axle pin I08 and a swinging sprocket I09 mounted on the end of alever III] which swings on a fulcrum pin III afiixed to the frame I04.The sprocket I09 is disposed at a greater distance from the pivot I05than is the sprocket IIJ'I, so that a pull in one direction upon thesprocket I09 will overcome a pull of equal force but of oppositedirection upon the sprocket I0'I and will cause the frame I04 to tilt inthe direction of the pull upon the sprocket I09. The lever III] has anarm II2 terminating in a dog I I3 engageable in a notch H4 in the basemember I06. The dog 3 is urged to engagement with the notch H4 by aspring II5 connecting the other arm of the lever IIO with the frame I04,and when so engaged, it prevents tilting of the frame I04 relative tothe base member I06. A chain IIE, which may be inserted in the cable 60shown in Figure 7 as a part thereof, traverses the sprockets I01 and I00so as to turn them in opposite directions. The portion II! of the chainH5 leading away from the sprocket I09 leads to shoulder harness or tocineplastic connections. The portion II8 of the chain leading away fromthe sprocket I01 leads to the lever 58, or to similar primary operatingmechanism of the prosthesis.

The sprocket I0! is provided with a brake I20 which may be expanded orcontracted by rotation of a triangular lever I2I having two of itscorners pivotally secured to the ends of the brake band I22. A link I23connects the third corner of the lever I2I to the arm 2 of the leverIIO. A second link I24 connects one end of the brake hand I22 and theattached corner of the lever I2| to the frame I04, thus providing afulcrum upon which the lever I2I may rotate.

As long as no resistance is encountered, the chain II-fi may run freelyover the sprockets I09 and I01, both of which will turn freely. When,however, a resistance or pull occurs on the end I I8 of the chain IIG,as would happen when the prosthesis grasps an object, there is aresulting tendency for the frame I04 to tilt relatively to the basemember I06. Tilting of the frame I04 9 will be momentarily prevented bythe engagement of the dog H3 in the notch H4, but if the resistance isof sufficient force, a continued pull upon the end II! of the chain I Itwill cause the lever II [I to rotate upon the fulcrum pin III,overcoming the resistance of the spring I I5. The initial rotativemovement of the lever IIE! pro ruces an upward pull on the link I 23,causing the triangular lever I2I to rotate and to set the brake I20;With the sprocket IIl'I no longer free to turn, and the chain IISconsequently held fast relatively to both sprockets, a further continuedpull upon the end I I! of the chain is transmitted directly to thespring I I5, causing the lever I III to rotate further and to disengagethe dog I I3 from the notch H4, as shown in Figure 15. The entireforce-multiplier then becomes a simple lever fulcrumed upon the pivotI85, producing a force multiplication in the ratio of the distances fromthe pivot I65 of the take-off points of the chain ends II! and H8 fromthe sprockets IilSand I07, with a corresponding reduction in the travelof the increased reaction.

In the modification shown in Figure 16, a cable I26 traverses pulleysI2! and I28, of which the pulley I2? is mounted directly upon a frameI29 and the pulley I29 is mounted upon a rod I30 which extends slidablythrough the frame I29 and is'urged outwardly by a spring ISI. Lock nutsI32 limit outward movement of the rod I'3Il relative to the frame I29and an adjustment nut I33 regulates the compressive tension on thespringI3I. The cable I26 may be'a part of the cable 65. The frame I29 istiltably mounted on a pivot pin I34 in a base I35. A lever I56, havingits fulcrum at the spindle I'3'Iof the pulley I 28, has oppositelyextending arms I 38 and I59. The arm I38 has a hooked end I 40engageable with a hook I4I on one end of a lever I42 pivoted on theframe I29. The other end of the lever I42 extends through the frame I29and presses upon a leaf spring I 43 securedto the base I35. The actionof the leaf spring I43 and lever I42 is to urge the lever I36 toclockwise rotation about its fulcrum point I31, as seen in Figure 16,but a stop IM acting upon the lever I42 limits the distance to which thelever M2 may follow the lever I56.

The pulley I21 has a brake I45, one end of which is held in relation tothe frame I 29 by a link I46, and the other end of which is attached tothe arm I39 of the lever I36 by a link I41. The link I4! is pivotallymounted on the frame I29 by a. pivot. pin I 4-8. and so serves as alever to operate the brake I45.

The operation of the modified form of forcemultiplier is in principlethe same as that described in connection with the preferred formillustrated in Figures 14 and 15. As long asthere is no resistance tothe pull on the cable I26, the pulleys: I 21 and I 28 rotate freely.Upon application of a sufficient resistance at'the end of the cabledeparting from the pulley I21, the pulley 528 is pulled towards theright (as viewed in Figure 16) against the resistance of the springI'3I. Such'movement of the pulley I25 not only movesthe. whole lever I36towards'the right, but causes it to rotate in clockwise direction, dueto pressure of the-lever I42 upon the hook I49. The link MT isconsequently rotated in clockwise directionv about the pivot pinI 48,causing the brake I45 to. tighten upon the pulley I21, When the pulleyI2! is restrained from rotating, theentire frame I29 will tilt upon thepivot pin I34 and becomea lever having the force ratio corresponding tothe distances from the pivot pin I534 Qf the 10 take-off points of thecable I26 from the pulleys I2'I'and I28. The hook I40 is swung out ofcontact with the lever I42 so that the spring I43 no longer affectsmovement of the frame I29.

In both the preferred and modified forms of force-multiplier, the latchmechanism provided in the one instance by the dog I I3 and notch I I4and in the other instance by the-hooks I40 and MI, holds the frame fromover-tilting in acounter-clockwisedirection when the tension on themuscle-motorend of the cable or chain .is relaxed. When the forcecausing the prosthesis to grip is abated, the spring 6-I moves thel'ever58 to cause a pull upon the cable 60 in the opposite direction,and such a pull would tend to tilt the forcemultipliertowards theprosthesis with resultant waste motion on the next application ofgripping tension, were it not for the action of the latch mechanism.

With the possible application of a grip of considerable power, asprovided by the locking'and grip tensing mechanism and by theforce-multiplier heretofore described, it becomes more than everdesirable to provide the amputee with means for sensing not only contactwith an object, but the pressure which his-prosthetic hand applies to anobject. We therefore prefer to include in our improved prosthesissensory devices of the kind illustrated in Figures 1'7to 20. In Figures17 and 18, we have illustrated a preferred form of sensory deviceindicating contactual pressure by tactile sensation and based onhydraulic principles of operation. A bladder I50 on the end of a fingerof the prosthesis, preferably the index finger 32, is connectedby aflexible tube I5I to a second bladder I52 held by suitable harness I53to the skin of the stump of the amputee, indicated at I54. The bladdersI58 and I52 have, respectively, flexible diaphragms I55 and I56, but areotherwise so rigid'as to be non-expandable. The flexible tube I5I may beof rubber but has a wall of such thickness and tensile strength as to benon-expandable. The bladders I50 and I52 and the tube I5I are filled tocapacity with a non compressible fluid, shown at I51 in Figure 18.Consequently, any pressure upon the diaphragm I 55 tends to dilate thediaphragm 56 and the pressure is transmitted to the skin of the amputeein proportion to its intensity at the finger tip. The tube I5I may bedisposed entirely within the fingers and casings of the prosthesis, tomaintain the esthetic appearance of the hand, and the prosthesis may becovered bv. a cosmetic glove without seriously impairing theeffectiveness of the sensory device. I

A sensory device modified to operate on electric principles isillustrated in Figures 19 and 20. A switch I58, of spring-resistedpush-button type, is attached to the end of a finger so as to close anelectric circuit IGI in response to finger-tip pressure. The circuitIfiI includes storagebatteries IGZAWhiCh may be located at anyconvenient point in the amputees clothing, and a vibrator disc H53attached by harness I64 to the skin of the amputees stump. Pressure atthe finger tip sufficient to closethe switchv IE0 is indicated to theamputee by thesensation of vibration on his skin. By making the switchIto. of the rheostat or variable bridge type, with its. movable'element:spring-urged to the high resistance end and thence toopen position,. thein.- tensity of vibration may be made to coincide with the intensity ofpressure.

When the amputee wishes to grasp an object with the prosthetic handherein. described. he

exerts tension upon the cable 69 by means of shoulder harness orcineplastic mechanism and so retracts the lever 58 and compresses thespring 6!. As heretofore described in detail, retraction of the lever 58causes fiexion of the prosthesis at the joint between the upper handcasing 25 and the digital casing 27, and also at the medial joints ofthe fingers 32 and 33. The hand is thereby caused to close upon theobject, and when contact with the object is attained, the sensory devicewill indicate the same by pressure or vibration upon the amputees stump.The resistance afiorded by the object will also bring into play theforce-multiplier, to the extent that it may be desired and feasible, andthe tension of the grip soproduced will be indicated to the amputee byincreased pressure or vibration upon his stump.

If the amputee wishes to hold the object for any'length of time, he willmove the bell crank lever 93 rearwardly, either with his other hand orby knocking it against some resistance, such as a table. If in hisestimation the grip upon the object. is already sufficiently tense, hewill move the bell crank lever through only such part of its arc ofmovement as will lock the prosthesis in the position already attained.If, however, he wishes to increase the tension of the grip or to lockthe grip more securely, he will move the bell crank lever to itsfurthermost rearward position. The amputee will learn, when handling anon-compressible object or a fragile one, to exert only moderate tensionby means of the force-multiplier, so that subsequent operation of thelocking mechanism neither strains the prosthesis nor crushes the objecthandled. In his estimation of the requisite tension he is, of course,guided in part by the sensory device.

To relax the grip, the amputee merely knocks the bell crank lever 93forward, if it has previously been moved rearwardly, and relaxes thetension-on the cable 59. The spring iii in the primary operatingmechanism, the springs 92 and I02 in the locking mechanism, and thesprings H5 or I3! in the force-multiplier then restore all moving partsautomatically to their open or relaxed positions.

It will readily be seen that the'greater part of all the operatingmechanism is disposed high up in the prosthesis towards the stump. Thesensory device is largely located upon the stump itself; the quickdisconnecting mechanism is centered at and above the wrist; theforce-multiplier is either within the stump cuff casing 46 or above iton the arm itself; and the locking and grip tensing mechanism is closelyadjacent to the wrist within the upper hand casing 25. The distalportion of the hand is therefore light in weight and not burdensome tothe amputee. The improved ball-and-socket joints by which it flexes arealso light and permit an increased articulation without adding to theweight. They also give the hand a more natural appearance than thecustomary tongue-and-groove joints and give better protection to theencased linkage. By having the index and middle fingers articulated toclose upon the thumb with a palmar grip, the most common articularmovement of the natural hand is closely simulated and is car riedthrough eihciently by the operating mechanism with little fatigue to theamputee.

We claim:

1. A prosthetic device for attachment to an arm stump, comprising anupper casing simulating the upper part of the human hand, a secondcasing simulating the digital portion of a hand, said casings havingmating semi-cylindrical end portions forming a substantially closedjoint and being pivotally secured to each other, a plunger in said uppercasing reciprocatably movable therein, means for connecting said uppercasing to said arm stump, lever means pivotally secured to said armstump, means connecting said lever means to a muscle motor, means foroperably connecting said plunger to said lever means when said uppercasing is connected to said arm stump, and linkage means connecting saidplunger to said second casing for flexing said joint in response tomovement of said plunger.

2. A prosthetic device for attachment to an arm stump, comprising anupper casing simulating the upper part and the thumb of a human hand, asecond casing simulating the digital por tion of a hand, including thethird and fourth fingers and the proximal phalanges of the in dex andsecond fingers, said upper casing having a transverse opening at itsdistal end and said second casing having a semi-cylindrical portionenlarged to fit within and mating with said transvers opening to form asubstantially closed joint and having an opening in saidsemi-cylindrica1 portion communicating with said transverse opening,additional casings simulating the distal portions of the index andsecond fingers and so shaped as to form ball-and-socket joints with theproximal phalanges of said fingers, a knuckle bar on said upper casingadjacent said transverse opening and having lugs extending through saidtransverse opening whereon said second casing is pivoted, movable meansactuable by muscular movement of the wearer, linkage principallydisposed within said upper casing and connecting said means with saidsecond casing for causing arcuate movement of said second casing inresponse to movement of said means, and additional linkage principallydisposed within said second casing and connecting said knuckle bar andsaid additional casings for causing arcuate movement of said additionalcasings in response to movement of said second casing.

JOHN E. CONZELMAN, JR. HERBERT B. ELLIS. CLAYTON W. OBRIEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 760,102 Carnes May 17, 19042,230,378 Eberle Feb. 4, 1941 2,464,577 Hobbs Mar. 15, 1949 2,427,974Otterman Sept. 23, 1947 FOREIGN PATENTS Number Country Date 315,024Germany Sept. 22, 1919 828,272 France Feb. 7, 1938 OTHER REFERENCESTerminal Research Reports on Artificial Limbs by Committee on ArtificialLimbs, National Research Council; received in Div. 55 of the PatentOfiice Nov. 13, 1947, pp. 87 and 88.

Artificial Limbs by Florent Martin, Geneva (1925), pp. 42 and 43. A copyis in Div. 55 of the Patent Ofiice.

